Fuel cells have developed as a method of generating electricity from chemicals. Some early development focused on using hydrogen as a clean fuel source for producing power. Work has been done on the storage and generation of hydrogen for use in fuel cells and is disclosed in U.S. Pat. Nos. 6,057,051, 6,267,229, 6,251,349, 6,459,231, and 6,514,478, all of which are incorporated by reference. Hydrogen is a high energy, low pollution fuel, however, the storage of this fuel is cumbersome, both from an energy density and safety point of view.
The difficulty of storing hydrogen has led to looking at the generation of hydrogen from more useful fuels. Liquid fuels containing a relatively high amount of hydrogen that can be generated through reforming have received significant attention. Reforming of a fuel is expensive, and adds significantly to the complexity and size of a unit using fuel cells for power generation. Reformers and methods of reforming liquid fuels have been developed, as shown in U.S. Pat. Nos. 4,716,859, 6,238,815, and 6,277,330, all of which are incorporated by reference. Therefore, there is significant interest in fuel cells that can use a hydrogen rich fuel that can be processed directly over a fuel cell electrode. This separates the fuel cells into two general categories: an indirect or reformer fuel cell wherein a fuel, usually an organic fuel, is reformed and processed to produce a hydrogen rich, and substantially carbon monoxide (CO) free feed stream to the fuel cell; and a direct oxidation fuel cell wherein an organic fuel is directly fed to the fuel cell and oxidized without any chemical reforming. Direct oxidation fuel cells can use either a liquid feed design or a vapor feed design, and preferably the fuels, after oxidation in the fuel cell, yield clean combustion products like water and carbon dioxide (CO2).
In early development of direct methanol fuel cells (DMFC), using gaseous methanol required a high heat, which brought about the degradation of the fuel cell membranes. This led to the development of DMFCs using methanol in the liquid phase, as shown in U.S. Pat. Nos. 5,599,638, and 6,248,460, and which are incorporated by reference. However, the liquid phase presents drawbacks also, not the least of which is cross over of the membrane by the methanol and contamination of the cathode.
As with vapor phase fuel cells, liquid phase fuel cells also have handling problems. Specific problems include the orientation of the fuel cells or portable devices such that liquid fuel can flow out of openings for releasing waste gases, and liquid fuel cells have the problem of the high concentration of liquid methanol permeating through to be oxidized at the cathode which reduces fuel cell efficiency.